Previous reports from our laboratory have proposed that taurine forms one member of a taurine-isethionic acid complex, the function of the complex being the regulation of membrane excitability of the heart cell. The substance taurine is in relatively high concentrations in myocardial tissue and increases under some pathological states (congestive heart failure) yet the exact pathway of taurine synthesis in the heart is not known. The present research seeks to define the metabolic pathway of taurine synthesis in dog heart. Radioactive labeled precursors will be incubated with dog heart slices and the timed appearance and intensity of radio-activity in intermediates will be determined. Conventional chromatographic separation procedures will be used. The intermediates will be quantitated by liquid scintillation counting and identified by chemical tests and infra-red absorption spectrometry.